1. Field of the Invention
The present invention relates to syringe type pumps having mechanisms therein or associated therewith for dispensing liquid at a very slow rate from the syringe barrel of the pump so as to meter the dispensing of liquid.
2. Description of the Prior Art
Heretofore various syringe devices and mechanisms associated therewith or incorporated therein for metering fluid from the syringe device have been proposed.
Examples of these previously proposed devices and mechanisms associated therewith are disclosed in the following U.S. Patents:
______________________________________ U.S. PAT. NO. PATENTEE ______________________________________ 2,474,496 Rayman 2,706,480 Nensel 2,875,761 Helmer et al. 3,325,061 Ellsworth 3,606,086 Drummond et al. 4,157,716 Ruegg 4,177,810 Gourlandt 4,190,048 Sampson 4,258,711 Tucker et al. 4,265,241 Portner et al. 4,274,558 Clausen ______________________________________
The Rayman U.S. Pat. No. 2,373,496 discloses a fluid injecting device having spaces between abutments or depressions on the plunger representing different units of volume of the contents within a syringe barrel of the device within which the plunger is received, which units are to be injected into a patient.
The Nensel U.S. Pat. No. 2,706,480 discloses an overdose preventing device mounted on a syringe in which a stop member is threadedly positioned within the syringe body to limit the maximum amount of fluid that can be drawn into the syringe body.
The Helmer et al. U.S. Pat. No. 2,875,761 discloses a multiple dosage syringe in which a dosage regulating device associated with the syringe has a pair of flexible legs engageable with recesses in the rear end portion of a plunger for enabling a user of the syringe to administer plural doses of equal volume.
The Ellsworth U.S. Pat. No. 3,325,061 discloses an hypodermic syringe having indicia on the syringe barrel and a slide member movable with a syringe plunger and having a forward end which indicates by its position relative to the indicia the amount of fluid dispensed from or withdrawn into the syringe barrel.
The Drummond et al. U.S. Pat. No. 3,606,086 discloses a microdispensing device wherein a series of recesses in a plunger holder are sequentially engageable by a spring detent so that a user may feel a click-like interengagement between the detent and the recesses as the plunger is moved into a syringe barrel whereby the user knows that a specified amount of fluid has been dispensed from or drawn into the syringe barrel. The plunger of the syringe works in conjunction with a capillary tube in effecting dispensing and withdrawing of liquid from or into the syringe barrel.
The Ruegg U.S. Pat. No. 4,157,716 discloses a motor driven liquid dose dispenser having two scaled rings movable relative to each other for indicating and limiting the quantity of liquid dispensed. One of the scale ring elements has a stop for limiting rotation thereof.
The Gourlandt U.S. Pat. No. 4,177,810 discloses a pneumatically operated automatic injection device for injecting liquids into animals.
The Sampson U.S. Pat. No. 4,190,048 discloses an infusate injection apparatus having a reservoir which is implanted in the human body and a pump which is also implanted in a human body. The pump is arranged so that it can be refilled as needed by simply injecting a fresh supply of infusate by means of a hypodermic needle through the patient's skin, through a pump septum and into the infusate chamber inside the apparatus. The act of refilling the pump can also serve to recharge a power supply or drive mechanism for the pump.
The Tucker et al. U.S. Pat. No. 4,258,711 discloses an implantable infusion apparatus having an infusate reservoir connected by way of a first flow path through a flow restricter to a mixing chamber and then into a vein. The reservoir and chamber volumes, the infusate concentration and chamber outlet flow rates are selected to provide an integrated dosage profile fitted to a patient. A restricter is provided and a drive capsule for the apparatus contains a compressible fluid such as a spring or two phase liquid for causing dispensing of liquid such as insulin into a patient's vein at a predetermined rate. The infusion apparatus is non-electrical.
The Portner et al. U.S. Pat. No. 4,265,241 discloses an implantable infusion device wherein a reservoir is defined by a bladder received in a chamber and the reservoir chamber can be pressurized by means of vapor pressure or a mechanical spring with a drug such as insulin under pressure in the reservoir being released in response to an externally applied electrical signal via a solenoid.
The Clausen U.S. Pat. No. 4,274,558 discloses a device for dispensing a liquid by use of a peristaltic type pump acting on a tubing.
As will be described in greater detail hereinafter, the pump of the present invention differs from the previously proposed dispensing, metering and pumping devices by providing a simple piston and cylinder type pump wherein the piston rod of the pump is driven by a gas spring.
Further, a dampening or timing mechanism is associated with the piston rod for dampening axial movement thereof whereby liquid is dispensed or metered from a syringe barrel at a predetermined rate to provide a desired basal dispensing or metering of liquids such as insulin, heparin or the like.
Still further, the pump of the present invention can be provided with a bolus control mechanism for providing a bolus infusion of a liquid, such as a drug or insulin, when such is needed, such bolus control mechanism being adapted to override a basal delivery system of the pump and yet permit the basal delivery system to continue to function after a bolus infusion.